Method and apparatus for regulating consistency



Feb. 13, 1962 D. A. FEIGLEY, JR 3,020,765

METHOD AND APPARATUS FOR REGULATING CONSISTENCY 2 Sheets-Sheet 1 PREPARATION Filed March 15, 1957 STOC K PREPARAT lON I DEAERATION I I DEAERATION I WElGHT-VOLU ME WEIGHTI-VOLUME DETERMINATION DETERMINATION CONSISTENCY ADJUSTMENT CONSISTENCY ADJUSTMENT \F NEEDED IF NEEDED I PAPER FORMING I I PAPER FORMING I INVENTOR DAVID A. FElGLEY, JR.

ATTORNEY Feb. 13, 1962 D. A. FEIGLEY, JR

METHOD AND APPARATUS FOR REGULATING CONSISTENCY Filed March 15, 1957 2 Sheets-Sheet 2 INVENTOR DAVID A. FElGLEY, JR.

ATTORNEY United States Patent 3,020,765 METHOD AND AlPARATUS FOR REGULATING CQNSISTENCY David A. Felgley, Jr., Manor Township, Lancaster County, Pa, assignor to Armstrong Cork Company, Lancaster, Pan, a corporation of Pennsylvania Filed Mar. 15, 1957, Ser. No. 646,247 6 Claims. (Cl. 73-434) This invention relates to a method and apparatus for regulating consistency. More particularly, the invention relates to improvements in existing methods and apparatus for the regulation and determination or" the consistency of the stock from which paper and similar products are made.

Paper stock or pulp is delivered to the proportioning meters, refiners, Fourdrinier wire, or other papermaking machines as a stock or pulp which contains relatively small proportions by Weight of the solid constituents such as fiber, fillers, and the like suspended in water.. The amount by weight solids-termed the consistency, generally will vary from about 0.5% to about 15%, depending on the type of pulp being handled. It is important that in any given run in the papermaking process there be as little variation as possible in the stock delivered to the proportioning meters, the refiners, or the paperforming machine in order to produce a uniform product. It is apparent, therefore, that the consistency of the stock fed to these machines must be kept under control in order that a uniform and suitable product be continuously made. There are a great many other variables which must be controlled too, but this invention is primarily concerned with the control of the consistency.

It has been proposed in the past in the general literature and in the patent literature to determine and to regulate the consistency of the stock by measuring the weight of a fixed volume of the stock. Knowledge of the precise weight of a precise volume containing fibers of a known specific gravity suspended in water at a known temperature is all the information that is needed to determine the percentage by weight solids-the consistency-of the stock. Accordingly, prior workers in the art have developed ingenious devices which, on suitable calibration, indicate a variation in weight of a fixed volume of the stock. This variation is a measure of the change in the consistency of the stock and, accordingly, the variation may be corrected by manual or automatic control.

This approach to consistency regulation rests on a sound theoretical basis, yet a great deal of trouble has been encountered in attempting to make the technic work in practice. The primary difiiculty appears to lie in the impossibility of measuring precise volumes. The accuracy of weighing devices surpasses the accuracy of volumetric devices.

As mentioned above, the percent by weight fibers in a papermaking slurry is very small. Therefore, weight and volume measurements must seek to determine small changes in the amount of the fibers which are already present in exceedingly small quantities. It is for this reason that slight changes in the volume of the slurry being measured give rise to anomalous results. The needed accuracy in the volume measurement is on the order of one part out of many thousands.

Despite these difiiculties, there are situations wherein the weight-volume determinations can be successfully used. These instances are confined to those cases wherein the fibers are present in a relatively large percentage by weight, and also where the fibers concerned have an unusually high specific gravity as is the case with asbestos, mineral wool, or glass fibers. It can be seen that where the total weight of the fibers constitutes an appreciable percentage of the total Weight of the slurry,

Patented Feb. 13, 1962 2 the accuracy requirements as to weight and volume are iminished. I

To illustrate this situation, US. Patent No. 2,746,- 475--Muench, issued May 22, 1956, is hereby incorporated herein by reference. The disclosure in that patent illustrates one modification of a weight-volume technic used to determine and regulate consistency. As that patent points out, however, its disclosure is primarily use ful where a heavy stock is used and where the consistency is on the order of 10% rather than 1%.

It is the principal contribution of the present invention to improve the accuracy of the methods and apparatus used in consistency determinations and regulation and based on determination of specific gravity of the stock. The present invention flows from the discovery that air, dissolved and entrapped in the slurry, destroys much of the accuracy which otherwise might be achieved in such consistency determinations.

Thus it is the primary object of the present invention to improve the accuracy of existing methods and apparatus for regulating consistency. It is a further object of the present invention to present a method and apparatus which will enable the carrying out of reasonably accurate consistency determinations on stocks having low consistencies. It is a further object to improve the accuracy of consistency determinations carried out on stock having high consistencies and in which the fibers have a high specific gravity.

To this end, the invention contemplates removing air bubbles adhering to the solids in a slurry, preferably a paper stock, and then determining the Weight of a fixed volume of the resulting deaerated slurry.

The removal of air from the stock may be carried out in any convenient manner. The stock may be passed through an evacuated chamber or may be treated with an air scavenging composition or compound such as diethyl ether. The entire volume of stock may be deaerated or merely a portion thereof, depending on convenience. Where an air scavenging composition is to be added to the stock to drive out the air, it may be impractical to treat the entire volume of stock, and hence it is preferred to split ofi a representative side stream and perform the consistency determination on the side stream. Side stream determinations may well be preferable where it is uneconomical to deaerate the entire stock supply being transferred to the paper-forming machine. However, where cheap vacuum is readily obtainable, deaeration of all the stock prior to its introduction into the head box of the paper-forming machine may also serve to improve the formation of the paper, and hence may be economically justified. The technic to be used in measuring the weight of a fixed volume of the stock may be adapted to particular circumstances and will be more fully discussed below.

It is ditficult to define the extent to which the air must be removed from the stock. It will be appreciated that the removal of any air from the stock will increase the accuracy of subsequent measurements to the extent of the removal of that amount of air. Yet to the extent that remaining air bubbles adhere to the solids in the slurry, to that extent subsequent weight and volume determinations will be inaccurate. Hence the extent of air removal is best defined as that amount which removes substantially all the air bubbles which adhere to the fibers in the slurry. If substantially all the air bubbles are removed, it follows that the air dissolved in the water will also be removed to a large extent. It is the air bubbles clinging to the fibers which cause the most difiiculty, and as those air bubbles are removed it may well be that dissolved air comes out of solution to form more bubbles which cling to the fibers. It is for these reasons that the amount of air to be removed to give the results contemaozoass plated by the present invention is defined as that amount of deaeration which substantially eliminates air bubbles adhering to the solids.

The inventive concept in the present invention is a simple but a far-reaching one. It is the carrying out of a weight-volume determination on a deaerated slurry. Such a combination has not been accomplished before, due apparently to a lack of recognition of the role played by dissolved and entrained air. Experimental Work has shown that weight-volume determinations carried out on nondenerated slurries give results so wildly erratic as to be completely useless. Yet where the stock has been sufficiently deaerated as to remove substantially all the air bubbles clinging to the fibers, results are improved to the point where they become meaningful. Specific conditions of deaeration are described in copending application Serial No. 646,197, filed concurrently herewith, wherein a completely different approach to the problem of consistency determination is fully described.

The invention will be further described with reference to the drawings, in which:

FIGURE 1 is a flow diagram illustrating one modification of the use of the present invention in a papermaking process;

FIGURE 2 is a flow diagram illustrating a modification of FIGURE 1;

FIGURE 3 is a simplified side elevation of one modification of apparatus illustrating the present invention; and

FIGURE 4 is a simplified side elevation of a modification of FIGURE 3.

Referring to the drawings, FIGURE 1 illustrates the situation where the entire flow of stock is deaerated and subjected to the weight-volume determination prior to the pumping of the stock to the head box of the paperforming machine. A consistency adjustment step may be carried out if needed by adding diluting water if the consistency is too high or a stock of higher consistency if the consistency is too low.

FIGURE 2 illustrates the modification of FIGURE 1 wherein a side stream is split oif from the main flow of stock to the head box of the paper-forming machine, and the side stream alone is subjected to deaeration and the weight-volume determination.

FIGURES 3 and 4 show two modifications of apparatus in which the present invention may be carried out. Other types of apparatus will occur to those skilled in the art. Although FIGURES 3 and 4 illustrate continuous apparatus in which to carry out consistency regulation, it will be recognized that batch type apparatus to be used only at the time a consistency determination is needed may also be utilized. Additionally, it should be pointed out that smaller samples may be physically withdrawn by hand and the necessary deaeration and volume-weight determination carried out on individual samples. In FIG- URES 3 and 4, like numbers refer to equivalent parts.

Referring specifically to FIGURE 3, the stock flowing in the header 1 is introduced by means of the inlet 2 to an evacuated chamber 3. A bafiie 4 shatters the incoming stream of stock in order that the vacuum may be more effectively applied thereto. The vacuum is applied to the chamber 3 by means of the vacuum line 5 which also serves to carry away air removed from the stock. The vacuum line 5 may be connected to a vacuum pump, steam jet, barometric leg, or other suitable means of applying vacuum, not shown. In order to substantially eliminate the air bubbles clinging to the fibers, it is preferred that the vacuum in a device such as that illustrated be at least about 21 inches of mercury. The level of stock inside the chamber 3 may be maintained at any point convenient for efiicient operation so as to prevent undue entrainment of liquid in the air stream moving through vacuum line 5.

The deaerated stock leaves the chamber 3 by means of the outlet 6 whereupon it is introduced into the weighing tank 7 by means of the weighing tank inlet 8. The weighing tank 7 is equipped with an overflow dam 9 over which the overflow pours into an overflow receiver 10. The weighing tank 7 will be equipped with an adjustable orifice 11 which may be nothing more than a valve adjusted to maintain a constant overflow over the overflow dam 9 and a constant underflow out of the orifice 11. The underflow pours into the underflow receiver 12, where the underflow joins with the overflow receiver 10 so that the underfiow and overflow may be returned to the production line.

The weighing tank 7 is rotatable around a knife edge or pin 13. The weight of weighing tank 7 filled with stock will be measured at 14, at which point will be positioned the sensitive element of a weighing device. In order that the weight as taken at 14 will not be influenced by the flow of incoming stock, a baflie 15 may be positioned at the bottom of the inlet 8. The entire arrangement yields the weight of a fixed volume of deaerated slurry and hence gives an accurate means of control or regulation of the consistency of the stock.

FIGURE 4 illustrates a type of weight-volume apparatus different from that illustrated in FIGURE 3. The weighing vessel 7, the inlet leg 8, and the weighing device 14 operate as in FIGURE 3. The outlet 11 and the frictionless flexible connections 16 constitute the prime difference from the apparatus of FIGURE 3. The frictionless flexible connections 16 may be fabricated from thin wall rubber hose, thin flexible metal, or any other suitable material.

Where the method and apparatus of the present invention are to be used as consistency regulators, it is necessary merely that the apparatus be calibrated against slurries having a known consistency. Where the method and apparatus are to be used to determine consistencies, it is advantageous that the specific gravity of the fibers under ambient conditions be known. As set forth more fully in aforesaid copending patent application Serial No. 646,197, the specific gravity of all cellulosic fibers which have been refined for papermaking purposes has been found to be 1.61 with room temperature tap water used for experimental purposes. This specific gravity will vary as the characteristics of the water change, but in each case it is a relatively easy matter to determine the specific gravity under the particular conditions encountered in the particular papermaking process.

I claim:

1. A method of determining the consistency of a papermaking slurry containing 0.5-15% by weight inorganic solids suspended in water, which comprises removing air bubbles adhering to the fibers in said slurry and determining the weight of a fixed volume of the resulting deaerated slurry.

2. The method according to claim 1 wherein said step of removing air bubbles is carried out by subjecting said slurry to a vacuum.

3. In a method of determining variations in the consistency of a papermaking slurry containing 05-15% by weight inorganic solids suspended in water by measuring the change in weight of a fixed volume of the slurry, the improvement which comprises deaerating the slurry prior to said measuring step to remove air bubbles adhering to the fibers in said slurry and carrying out said measuring step on said deaerated slurry.

4. The method according to claim 3 wherein said deaerating step is carried out by subjecting said slurry to a vacuum.

5. In a consistency regulating apparatus comprising a fluid-receiving tank adapted to maintain a fixed volume of slurry containing 05-15% by weight inorganic solids suspended in water, a slurry supply conduit discharging into said tank but out of contact with said tank, and means for weighing said tank when filled with slurry, the combination with said apparatus of evacuating means for removing air bubbles adhering to the solids in said slurry,

said evacuating means being positioned so as to deaerate References Cited in the file of this patent said slurry prior to the discharge of said slurry into said UNITED STATES PATENTS tank.

6. Apparatus for determining the consistency of a slur- 2,304,875 Bamhafl 1942 ry containing 05-15% by Weight inorganic solids sus- 5 M pended in water, which comprises a chamber adapted to FOREIGN P ATEN 1S maintain a fixed volume of a slurry, weighing means for 530 167 Great Britain 6 1940' determining the Weight of said chamber containing said 1 118636 France Man 1956 fixed volume, and means for deaerating the slurry so positioned as to discharge the deaerated slurry into said 10 chamber. 

